1. Field of the Invention
This invention relates to a porphycene compound useful as a dye, a pigment, a photoelectric functional material and a recording or storage material, in particular as a recording dyestuff for a large recordable optical recording medium whereby information can be recorded and/or reproduced using a blue and/or red laser beam. This invention also relates to an optical recording medium comprising the porphycene compound.
This invention also relates to an optical information recording medium comprising a recording layer capable of high-density recording where recording is particularly conducted using a blue-violet laser with a wavelength of 400 to 410 nm.
2. Description of the Related Art
It is well known that a CD-R (CD-Recordable) has been proposed and developed as a recordable optical recording medium complying to Compact Disk (hereinafter, referred to as CD) specifications and that it has been wide spread for music reproduction and an information terminal.
Generally, a near infrared semiconductor laser at 770 nm to 830 nm is used for recording and/or reproduction of the optical recording medium, where a signal is recorded on a recording layer made of, for example, an organic dye on a substrate in a heat mode. Specifically, when the recording layer is irradiated with a laser beam, optical absorption occurs so that the organic dye generates heat, by which a pit is formed in the recording layer. A recording signal can be detected from difference in a reflectance between areas with and without the pit during laser-beam irradiation.
Such a medium is compliant with CD specifications such as Red Book and Orange Book and is, therefore, characterized in that it may be interchangeably used in a CD and a CD-ROM players. The existing medium, however, has a recording capacity of about 680 MB, which is not adequate in the light of recording of a moving picture. Thus, there has been the need for a higher density and a larger capacity in an information recording medium as a quantity of information has been dramatically increased.
A higher density of a recording medium may be achieved by reducing a wavelength of a laser beam used in recording and reproduction and increasing a numerical aperture (N.A.) in an objective lens. There has been practically used a short wavelength laser at, e.g., 680 nm, 670 nm, 660 nm, 650 nm or 635 nm. Thus, reduction in a wavelength of a semiconductor laser, increase of an N.A. in an objective lens and a data compaction technique have allowed us to obtain an optical recording medium capable of recording a moving picture or a large quantity of information. Consequently, a recordable digital versatile disk (hereinafter, referred to as DVD-R) has been developed as a recordable optical recording medium in response to the above laser beam. A DVD-R is an optical recording medium with a recording capacity of 3.9 GB or 4.7 GB which is writable only once. There has been further the need for developing an optical disk exhibiting good recording properties suitable to the capacity. A red laser used in the medium has a wavelength of 550 nm to 700 nm, preferably about 635 nm to 660 nm. Optical recording media which have been suggested for the conditions include magneto-optical media, phase-change recording media, chalcogen-oxide optical recording media and organic-dye optical recording media. Among these, organic-dye optical recording media might be preferable in the light of their lower cost and good processability.
Recordable optical recording media comprising a recording layer in which a dye is employed and a reflecting layer formed on the recording layer for improving a reflectance have become widely marketed as recordable compact disks (Compact Disk Recordable; CD-R) employing a cyanine or phthalocyanine dye in a recording layer since they have been disclosed in, for example, Optical Data Storage 1989 Technical Digest Series Vol. 1, 45 (""89). These media may permit recording with a semiconductor laser at 780 nm and the data may be reproduced by a widely marketed CD or CD-ROM player equipped with a semiconductor laser device at 780 nm.
Furthermore, DVD-R media with a capacity of 4.7 GB in one side have been recently marketed as an optical recording medium with a higher density than a CD and capable of recording and reproduction of a moving picture with TV quality, in which recording is conducted using a red semiconductor laser with an emission wavelength of 635 to 660 nm and which can be reproduced by a growing commercial DVD video player or DVD-ROM player. Such a DVD-R medium also employs a lamination structure where a dye such as a cyanine and an azo dyes is used in a recording layer and a reflecting layer is formed, having a disk structure where two substrates with a thickness of 0.6 mm are laminated.
It is expected that much higher recording will be in future required, resulting in a larger capacity of 15 to 30 GB. It may be, therefore, inevitable to use a laser with a much shorter wavelength to achieve such a recording density. Therefore, a dye exhibiting good recording properties within a wavelength range of 300 to 500 nm will be required as a recording dye used in a future organic-dye type of optical recording medium.
In terms of a medium which can conduct higher-density recording than a DVD-R using an organic dye as a recording layer, JP-A 10-302310 has disclosed that a laser with an emission wavelength of 680 nm or less may be used to achieve a density corresponding to a recording capacity of 8 GB or more. The publication has suggested that a laser at 680 nm or less may be focused using an objective lens having an N.A. of 0.7 or more through a light transmitting layer with a thickness of 10 to 177 xcexcm to achieve recording with a large capacity of 8 GB or more.
Meanwhile, there have been, as a blue laser, developed a laser at 410 nm using a GaN material and a SHG laser at 425 nm which is a combination of a semiconductor laser and an optical waveguide device (See e.g., Nikkei Electronics No.708, p.117, Jan. 26 (1998)). There have been attempts for developing a dye for a blue semiconductor laser in response to such a laser.
Since Nichia Corporation distributed samples of a GaN semiconductor laser with blue-violet emission at an emission wavelength of 390 to 430 nm from the beginning of 1999, there has been investigated a medium which has a further higher density capacity of 15 GB or more in one side and can record a moving picture for about 2 hours with an HDTV (high definition television) broadcasting quality (hereinafter, referred to as an xe2x80x9cHD-DVD-R mediumxe2x80x9d). Such an HD-DVD-R medium with a high density capacity allow us to conduct recording for about 6 hours with image quality in current broadcasting. It has been, therefore, paid much attention as a new recording medium in place of a home VTR. A technical review of a medium using an inorganic recording film made of a phase change material has been published in Nikkei Electronics, No. 751, p.117, Sep. 6 (1999).
To date, dyes recordable with a blue laser at 400 nm to 500 nm include cyanine dyes described in JP-As 4-74690 and 6-40161; porphyrin dyes described in JP-As 7-304256, 7-304257, 8-127174 and 11-334207; polyene dyes described in JP-As 4-78576 and 4-89279; azo dyes described in JP-As 11-334204 and 11-334205; dicyanovinylphenyl dyes described in JP-A 11-304206; coumarin compounds described in JP-A 2000-43423; and pyrimidine compounds described in JP-A 2000-163799.
Other examples include an optical recording medium described in JP-A 11-53758 comprising two layers, i.e., a recording layer mainly containing, e.g., a porphyrin dye or cyanine dye as an organic dye for forming a recording layer and a metal reflecting layer mainly containing silver; an optical recording medium described in JP-A 11-203729 with an improved medium configuration which has a blue-laser sensitive dye layer comprising a cyanine dye responding to a blue laser and a red-laser sensitive dye layer to allow us to conduct recording in two wavelength regions; an optical recording medium described in JP-A 11-78239 using an indigoid dye in which two dyes for a blue and a red lasers are mixed to allow us to conduct recording in two wavelength regions; an optical recording medium described in JP-A 11-105423 using a cyanoethene dye; and an optical recording medium described in JP-A 11-110815 using a squalirium dye.
Furthermore, JP-As 7-304256 and 7-304257 have described as an example of recording using an organic dye film in a blue range of 400 to 500 nm that a porphyrin compound is mixed with a molecular compound and a polymer coordinating to a central metal in the porphyrin compound or a polymer having a side chain coordinating to the central metal to make the Soret band in the porphyrin compound shift to a longer wavelength side for an Ar laser at 488 nm while allowing a film to be formed by spin coating. According to our investigation, polyene dyes such as those described in JP-As 4-78576 and 4-89279 have poor light stability and require improvement such as blending of quenchers for practical use.
Optical recording media recordable to both wavelength-region lasers include optical recording media using a porphyrin compound described in JP-A 10-101953 and a tetraazaporphyrin dye described in JP-A 11-144312. Specifically, porphyrin compounds and azaporphyrin dyes having a similar structure exhibit an absorption called as the xe2x80x9cQ bandxe2x80x9d in a longer wavelength side in the visible region and also a strong absorption called as the xe2x80x9cSoret bandxe2x80x9d in a shorter wavelength side in the visible region. The publication has implied that a circular organic compound such as porphyrin widely used in a dye, pigment, photoelectric functional material or so on may be a compound having properties as a dye for a DVD-R as well as an optical recording medium by which higher-density recording can be conducted in response to 15 to 30 GB.
Recently, since practical use of a blue-violet laser with a wavelength of 400 nm to 410 nm has become feasible, large-capacity recordable optical recording media using the laser have been intensely developed, and in particular, there have been the need for developing a dye exhibiting good light resistance and good rapid-recording properties.
The above optical recording medium for a blue semiconductor laser is, however, inadequately suitable to a laser beam at a wavelength of 400 nm to 410 nm. Specifically, we have found, for example, a problem that a medium using the organic dye does not necessarily give a good ratio between a carrier wave and a noise (C/N) for reproduction of a recorded signal, sometimes leading to unsatisfactory signal reading. It has become urgent to develop an optical recording medium capable of recording and reproducing with a higher density using a laser beam at a wavelength of 400 nm to 410 nm by solving the problem. Furthermore, it is essential to incorporate an organic dye responding to a laser wavelength of 635 nm to 660 nm in a recording layer for accommodating a DVD-R with a capacity of 4.7 GB strongly needed as a recording/reproducing medium for a digital moving image. The objective cannot be achieved only by the above recording dye exclusively for a blue laser wavelength.
Furthermore, an optical recording medium described in JP-A 11-203729 capable of recording and reproducing in two wavelength regions, i.e., a blue and a red laser wavelength regions, must have a plurality of recording layers. An optical recording medium described in JP-As 11-78239, 11-105423 and 11-110815 must comprise at least two recording dyes, leading to a complicated preparation process for the medium and there is a room for improvement in recording properties. An optical recording medium described in JP-As 11-101953 and 11-144312 has not been optimized for recording/reproduction using each laser beam selected within both wavelength regions of 400 nm to 410 nm and 635 nm to 660 nm.
We have investigated recording materials suitable to a recordable optical recording medium and have finally found the followings:
(1) Since a large-capacity recordable optical recording medium employs a laser beam at 300 to 500 nm and/or 500 to 700 nm for writing and reading a record, it is important that a recording material is controlled for its absorption coefficient, refractive index and reflectance near a laser wavelength;
(2) There have been intensely developed large-capacity recordable optical recording media using the laser and in particular, there has been the need for developing a dye exhibiting good light resistance and good high-speed recording properties. The above dye as a recording material recordable and reproducible to a laser within these wavelength regions, however, has not exhibit adequate properties and there are a room for improvement. Furthermore, preparation of a medium by an application process such as spin coating in which a recording film may be readily formed has an advantage that it exhibits higher solubility in an applied solvent and thus the advantage must be also considered.
It is generally necessary to conduct higher-density recording for increasing a recording capacity. It is, therefore, essential to increase an N.A. for an objective lens for focusing an optical beam used for recording and to reduce a wavelength of a laser beam in an optical system. A minimum beam diameter in the focused optical beam depends on a diffraction limit.
Meanwhile, since recording is conducted when a beam intensity exceeds a threshold, a recording pit smaller than a focused beam spot is formed as seen in FIG. 6(a). The area surrounding the pit corresponds to the periphery of the intensity peak. As a wavelength becomes shorter, the periphery of the recording pit tends to accelerate a photochemical reaction of the recording layer. Particularly, the above wavelength region of a blue-violet laser becomes a wavelength region where a photochemical reaction of an organic compound easily occurs, leading to problems of deterioration in a pit edge during recording and poor signal properties. Specifically, as shown in FIG. 6(b), recording information which must be ideally formed in response to a rectangular wave (the solid line in FIG. 6(b)) exhibits a broad waveform (the broken line in FIG. 6(b)) due to deterioration in a pit edge. There is also a problem that when using the same blue-violet laser wavelength as that in recording, even a weak irradiation like a reproduction light may accelerate a photo reaction to promote deterioration after each reproduction. JP-As 7-304256 and 7-304257 have taken a measure that a reproduction light has a different from, substantially longer than, a recording light. Thus, the requirement of a higher density cannot be adequately met. The use of a recording and a reproduction lights with different wavelengths means that a recording and a reproduction devices must be separately prepared or one device must have two optical systems and their control systems, which may lead to limitation in applications as an optical recording medium, a larger apparatus, an increased cost and thus poor utility. Furthermore, in a conventional optical recording medium such as a CD-R, ON/OFF of recording has been controlled through an explicit thermal threshold in a physical property such as a melting point, a sublimation point, a phase transition point or a thermal decomposition point of an organic dye film. Involvement of optical deterioration mode due to blue-violet-laser excitation make the contrast obscure. In particular, it may significantly deteriorate recording signal quality in a high-density recording system where a minute recording pit smaller than an optical beam must be formed.
An objective of this invention is to provide an optical recording medium capable of high-quality optical recording and reproduction by preparing an optimal dye for recording/reproduction of information using a light.
We have intensely attempted for solving the above problems and have finally achieved this invention.
Specifically, this invention provides the followings.
(1) An optical recording medium having a recording layer comprising at least one compound selected from optionally metal-complexed porphycenes.
(2) The optical recording medium having an organic dye layer as a recording layer on a substrate, comprising at least one compound selected from the compounds as defined in the above (1) in the organic dye layer.
(3) The above optical recording medium wherein the compound is represented by general formula (1): 
wherein the rings A, B, C and D independently represent an optionally substituted pyrrole ring; X1, X2, X3 and X4 independently represents optionally substituted methine group; and M represents two hydrogen atoms, a bivalent to tetravalent metal, metalloid or oxymetal atom optionally having a substituent or ligand.
(4) The above optical recording medium wherein the above compound is represented by general formula (2): 
wherein R1 to R12 independently represent hydrogen, halogen, nitro, cyano, hydroxyl, amino, carboxyl, mercapto, substituted or unsubstituted alkyl, aralkyl, aryl, alkenyl, alkoxy, aralkyloxy, aryloxy, alkenyloxy, alkylthio, aralkylthio, arylthio, alkenylthio, acyl, acyloxy, mono-substituted amino, di-substituted amino, alkoxycarbonyl, aralkyloxycarbonyl, aryloxycarbonyl, alkenyloxycarbonyl, mono-substituted aminocarbonyl, di-substituted aminocarbonyl, heteroaryl or heteroaryloxy; or each substituent of R1 to R12 together with an adjacent substituent may form a ring through a linking group; and M1 represents two hydrogen atoms, a bivalent to tetravalent metal, metalloid or oxymetal atom optionally having a substituent or ligand.
(5) The above optical recording medium wherein the above compound is represented by general formula (3): 
wherein R13 to R24 independently represent hydrogen, halogen, nitro, cyano, hydroxyl, amino, carboxyl, mercapto, substituted or unsubstituted alkyl, aralkyl, aryl, alkenyl, alkoxy, aralkyloxy, aryloxy, alkenyloxy, alkylthio, aralkylthio, arylthio, alkenylthio, acyl, acyloxy, mono-substituted amino, di-substituted amino, alkoxycarbonyl, aralkyloxycarbonyl, aryloxycarbonyl, alkenyloxycarbonyl, mono-substituted aminocarbonyl, di-substituted aminocarbonyl, heteroaryl or heteroaryloxy; each of R13 to R24 together with an adjacent substituent may form a ring through a linking group; M2is a bivalent to tetravalent metal atom having a substituent selected from the group consisting of alkyl, aryl and heteroaryloxy group and/or a ligand selected from the group consisting of a carbon monoxide and an alcohol.
(6) The above optical recording medium capable of recording and reproduction to a laser beam with a wavelength selected from the range of 300 nm to 500 nm and/or 500 nm to 700 nm.
(7) The above optical recording medium capable of recording and reproduction to a laser beam with a wavelength selected from the range of 400 nm to 500 nm and/or 600 nm to 700 nm.
(8) The above optical recording medium capable of recording and reproduction to a laser beam with a wavelength selected from the range of 400 nm to 410 nm and/or 635 nm to 660 nm.
(9) A compound represented by general formula (1): 
wherein the rings A, B, C and D independently represent an optionally substituted pyrrole ring; X1, X2, X3 and X4 independently represents optionally substituted methine group; and M represents two hydrogen atoms, a bivalent to tetravalent metal, metalloid or oxymetal atom optionally having substituents or ligands.
(10) The above compound represented by general formula (2): 
wherein R1 to R12 independently represent hydrogen, halogen, nitro, cyano, hydroxyl, amino, carboxyl, mercapto, substituted or unsubstituted alkyl, aralkyl, aryl, alkenyl, alkoxy, aralkyloxy, aryloxy, alkenyloxy, alkylthio, aralkylthio, arylthio, alkenylthio, acyl, acyloxy, mono-substituted amino, di-substituted amino, alkoxycarbonyl, aralkyloxycarbonyl, aryloxycarbonyl, alkenyloxycarbonyl, mono-substituted aminocarbonyl, di-substituted aminocarbonyl, heteroaryl or heteroaryloxy; or each substituent of R1 to R12 together with an adjacent substituent may form a ring through a linking group; and M1 represents two hydrogen atoms, a bivalent to tetravalent metal, metalloid or oxymetal atom optionally having substituents or ligands.
(11) The above compound represented by general formula (3): 
wherein R13 to R24 independently represent hydrogen, halogen, nitro, cyano, hydroxyl, amino, carboxyl, mercapto, substituted or unsubstituted alkyl, aralkyl, aryl, alkenyl, alkoxy, aralkyloxy, aryloxy, alkenyloxy, alkylthio, aralkylthio, arylthio, alkenylthio, acyl, acyloxy, mono-substituted amino, di-substituted amino, alkoxycarbonyl, aralkyloxycarbonyl, aryloxycarbonyl, alkenyloxycarbonyl, mono-substituted aminocarbonyl, di-substituted aminocarbonyl, heteroaryl or heteroaryloxy; each of R13 to R24 together with an adjacent substituent may form a ring through a linking group; M2 is a bivalent to tetravalent metal atom having a substituent selected from the group consisting of alkyl, aryl and heteroaryloxy group and/or a ligand selected from the group consisting of a carbon monoxide and an alcohol.
According to this invention, a porphycene compound of this invention may be used as a dye for a recording layer to provide a recordable optical recording medium capable of recording and reproduction by a laser at 300 to 500 nm, particularly a blue-violet laser at 400 to 410 nm which has drawn much attention in terms of a high-density optical recording medium, as well as capable of recording and reproduction at 500 to 700 nm used for recording a moving picture for two or more hours such as a movie.